The present invention relates to a counter rail and to a combination module of a counter rail and a dolly respectively, suitable for use in an apparatus for heat sealing a laminated packaging material for packaging of a liquid or flowing product.
The invention also relates to an apparatus for heat sealing and to a sealing/cutting apparatus including said counter rail and dolly, as well as to a packaging machine including such a sealing apparatus and counter rail and dolly of the invention.
Furthermore, the invention relates to a method of producing said counter rail and dolly.
Food packaging processes of today (with the term xe2x80x9cfoodxe2x80x9d is meant all sorts of solid and liquid food, such as juices, milk and other beverages as well as pastes, soups, jellies and cheese) often are of the type xe2x80x9cform-fill-sealxe2x80x9d and may be carried out by shaping a continuously moving web-shaped packaging material made of a flexible laminate into a continuously running tube, continuously filling the tube with the desired food product to be packaged and by sealing and finally cutting off sealed packages from the tube. An example of such forming of a tube from a continuous web of packaging material and the further formation of packaging containers is schematically shown in FIG. 1a. 
The packaging processes are often high speed continuous processes, wherein the packaging material in the form of a web is continuously fed through a machine, sterilised, for example by passing through a liquid or gas-phase quick-acting sterilising medium, formed and sealed into the required tube-shape for being filled with the food to be packaged and finally transversally sealed.
The continuous web-shaped packaging material is manufactured with a packaging material manufacturing machine and placed on a reel. The packaging material often has a laminated structure comprising a core layer of paper or paperboard, an outer heat sealing layer of a thermoplastic polymer (such as for example polyethylene) on each side of the core layer and, if necessary, an aluminium foil gas-barrier layer interposed between the paper core layer and the film. Alternatively, a gas-barrier layer of a plastics or inorganic material, such as for example polyamide, polyethylene vinylalcohol (EVOH) or siliconoxide, may be employed instead of aluminium foil.
The reel with packaging material is installed in the packaging machine where it is reeled out and routed within the packaging machine using drive mechanisms disposed in several positions in the machine. The packaging material web is shaped into a tube and sealed in the longitudinal direction within the packaging machine. While the tube is being transferred downward within the packaging machine, the liquid or flowing food product is supplied from above to fill the inside of the tubular packaging material. Next, the packaging material tube is squeezed laterally from both sides and sealed in the lateral direction at specified intervals to form interconnected, filled and sealed packaging containers. Next, the sealed packaging containers are separated off from the tube by cutting between the laterally extending sealed portions, and the thus separated packaging containers are brought into a specified, desired shape, for example by folding and bending along previously formed crease lines in the packaging material, and, if required, finally sealed in order to remain in that shape.
The sealing of the tubular packaging material in the longitudinal or lateral direction is carried out by heat sealing of the outer surfaces of the packaging material, which are made of heat sealing thermoplastics, to each other. This may be performed by known heat sealing techniques, such as for example induction heat sealing, radio frequency (RF) or microwave heat sealing, heat convection sealing or ultra-sonic vibration heat sealing. A very common heat sealing technique today for the transversal heat seals in the case of aseptic packaging, is the induction heat sealing, wherein the aluminium foil in the packaging laminate co-acts with an inductor in order to generate heat. The thermoplastic surfaces are bonded to each other by heat fusion by simultaneous application of the induction current and pressure.
Alternatively, packaging processes may often be of the type that are forming packages from pre-cut blanks of packaging material. An example of a principle for such 6 packaging process is shown in FIG. 1b. 
Pre-cut blanks of packaging material may be fed into a packaging machine, folded and longitudinally sealed, fold-formed and sealed at the bottom in order to provide open package capsules. The capsules are filled and subsequently sealed at the top, thus providing filled packages (11xe2x80x3).
Conventional packaging machines thus employ a heat sealing apparatus to seal the packaging material. The sealing apparatus is normally provided with so-called counter jaws and heat seal jaws disposed and working in opposing relation to each other.
An example of such a heat sealing apparatus is schematically shown in FIG. 4, while a cross-section view of a typical counter jaw and a heat-seal jaw is schematically shown in FIG. 5.
Conventionally, for transversal heat sealing, each counter jaw is provided with a pair of counter rails, while each heat-seal jaw is provided with a sealing block. Each counter rail and oppositely facing seal block are capable of creating one transversal heat seal across the packaging material. A cutter may be disposed in the gap formed between the two counter rails. Each cutting rail is provided with a counter element, a so-called xe2x80x9cdollyxe2x80x9d or xe2x80x9cpressure padxe2x80x9d, that extends along the counter rail, while the sealing block, in the case of induction sealing, is provided with an inductor coil disposed opposite to the dolly. Most commonly, in the case of packaging into a continuous tubular packaging material, the sealing and cutting operations are performed in the same part of the pack aging process, in which cases the counter rail is also called xe2x80x9ccutting railxe2x80x9d. However, it is also fully possible to separate the sealing and the cutting operations from each other, for example by subsequently cutting the filled and sealed tube in a separate cutting unit.
FIGS. 2 and 3, schematically illustrate a side-view of a conventional counter rail and sealing block for induction sealing, disposed on opposite sides of the packaging material to be heat sealed, before and after the sealing has been carried out.
As shown in FIGS. 2 and 3, the packaging material walls 12,13 of a tube or capsule may be placed in face to face relation to each other in a sealing zone S, for transversal induction sealing of the for example tubular packaging material 11. Each of the packaging material walls 12,13 is normally of a laminate structure made up of a paper base layer 14, and a film layer 16 of polyethylene, for example, located on the inside surface of the aluminium foil layer 15. Although not specifically illustrated, the outside surface of the paper base layer 14 is also coated with a layer of plastics material such as polyethylene. The polyethylene portions 16 of the two packaging materials 12, 13 are bonded together by heat fusion.
In other heat sealing methods, such as in high frequency (RF) sealing or heat convection sealing, an aluminium foil layer is not needed for the generation of heat.
The counter rail 21 normally is made of steel, and fulfils the requirements on planarity and parallelism. Depending on i.a. the requirements of the seal quality, the type of packaging material, the size of the package and the type of product to be packed, the shape and mechanical properties of the dolly 22 may be varied to suit the circumstances best. In the case of high quality seals as in the case of the present invention, such as for example for aseptic or long-term storage, so-called xe2x80x9cextended shelf-lifexe2x80x9d packaging, the dolly needs to have some degree of flexibility and compressibility for control of the flow of the heated thermoplastics from the layer 16 in the seal zone S. For packages with less stringent requirements on the seal quality, the dolly may be made of a durable hard metal material, just like the counter rail.
The inductor coil 23 extends along the sealing block 24 and is normally provided with a projection 25 extending toward the counter jaws. A coolant passage 26 is formed through the inductor coil 23 to control the temperature of the inductor coil 23 as a result of coolant flowing through the coolant passage 26.
In the initial stages of the sealing process shown in FIG. 2, the packaging material 11 is placed between the sealing block 24 and the counter rail 21 with dolly 22, whereupon the counter jaw and the heat seal jaw are moved so that they approach each other. Subsequently, the counter jaw and the heat seal jaw are moved further towards each other, and the sealing portion of the packaging material 11 is pressed hard and deformed with the inductor coil 23 and the counter element 22. A high frequency voltage is applied with a power device (not shown) to cause the aluminium foil 15 to generate heat with induction current. As a result, as shown in FIG. 3, the paired polyethylene portions 16 of the packaging material facing each other and squeezed between the paired aluminium foils 15 are heated and the polyethylene portions 16 in the sealing zone S are fused. Consequently, the tubular packaging material 11 is bonded together by heat fusion.
As shown in FIG. 3, the compressible counter element 22 is deformed during the sealing stage. When the pressure from the sealing block and the counter rail is released, the counter element is resuming its original shape and is ready for the next sealing and compression operation. Such compressible counter elements are conventionally made of a plastics material with suitable mechanical and chemical properties. Today, most commonly a cross-linked polyurethane (PUR) is used for this purpose. The desired shape and configuration of the dolly is usually cut out from a cross-linked polyurethane material. The dolly of cross-linked PUR is fastened into the cutting rail of stainless, chemically resistant steel by insertion into a groove 27 extending along the counter rail 21. The configuration, hardness and compressibility of the dolly are factors of great importance to the quality of the seal, and may vary depending on the various factors listed above, i.e. required seal quality, type of packaging material, package size and product to be filled. Different shapes and hardness/compressibility proper-ties of the dolly will influence the flow of thermoplastics in the seal zone S during heat fusion differently. Furthermore, these are important factors influencing the way in which the filled product in the tube is squeezed away from the sealing zone S. Different shapes have thus proved to be optimal for different combinations of package sizes and products to be filled.
Furthermore, the plastics material used in the dolly should be resistant to chemicals (for example alkaline cleaning agents, lactic acid and other substances in various filling products and to sterilisation agents, such as for example hydrogen peroxide (H202).
Although the known counter rail and dolly functions quite adequately, it does have a number of disadvantages. The main drawback with this known construction is that the dolly is made of a rather soft material in relation to the cutting rail and the sealing block, and will wear out after some time and thus must be exchanged for a new one with regular intervals. Each time the dolly is changed the packaging machine has to be stopped entirely. First, the counter rail has to be removed from the counter jaw, to which it is attached during operation. Then, the old dolly, which is fastened into the groove in the counter rail, has to be removed. When the old dolly has been removed, a new fresh dolly must be inserted into the narrow groove of the counter rail and subsequently the counter rail has to be attached to the counter jaw and the machine started up again. The groove, as well as the dolly, usually has an asymmetrical cross-section configuration and it is important that the dolly is carefully fastened and secured into the groove and that it is inserted in the right position, i.e. oriented in the right way. The steps of changing the dolly take some time, since the dolly should be quite strongly fastened into the groove and the dolly, therefore, has a slightly larger cross-section than the groove. Accordingly, the dolly must be pulled out of, respectively pressed into, the groove by using some force. This is done manually, since it is a quite complicated operation. The time the machine has to be completely stopped may amount to up to about 10 minutes, including the slow-down and start-up time during which the machine is adjusted from/to normal operation speed, during which time at least 600-1300 packages could have been produced at normal production speed, depending on the type of packaging machine. Under time pressure, it is easy to insert the dolly in the wrong direction into the groove, which if not noticed in time results in that the seat quality will be decreased considerably and the machine will have to be stopped completely a second time and, thus, in considerable extra losses of efficient production time.
Furthermore, when removing the dolly from the counter rail, sometimes it is tempting to use a pointed tool such as a screw-driver in order to get grip of the dolly and pull it out. Under unfortunate circumstances, this may damage the counter rail also. Since a new counter rail of steel is quite costly, this is highly undesirable.
Another disadvantage with the known construction of the counter rail and dolly is that the two parts of the module, i.e. the counter rail and the dolly, are made of different materials having considerably different thermal expansion coefficients. Plastics normally have thermal expansion coefficients ranging from about 100 to about 200 10xe2x88x925 mKxe2x88x921, while the coefficients of metals vary from about 6 to about 10 10xe2x88x925 mKxe2x88x921. When the heat sealing is carried out and the dolly is heated, it expands much more and much faster than the counter rail at the same temperature. The dolly therefore needs some space around itself inside the groove for expansion, and also must be able to move and slide against the inside surface of the groove. Thus, the shape of the dolly is critical from several points of views, i.e. firstly for the squeezing and pressing properties in the seal zone and secondly for enabling secure attachment within the groove when cold as well as thermal expansion within the groove of the counter rail when hot. This makes the counter rail provided with a dolly a very complex module of parts, both in view of manufacturing and in view of assembling.
There is thus a need for a counter rail and a combination module of a counter rail and a dolly respectively, that is not susceptible to the disadvantages, drawbacks and problems associated with a conventional counter rail or counter rail module. In particular, it would be desirable to provide a combination of counter rail and dolly that functions equally well as conventional ones, but have the further advantages of being easily and quickly interchangeable in the sealing apparatus and packaging machine, preferably at lowered or at least maintained cost levels.
It is, therefore, an object of the present invention to provide a counter rail to be provided with a dolly and such a combination module respectively, which overcomes or alleviates the above mentioned problems.
It is accordingly an object of the invention to provide a counter rail to be provided with a dolly, which enables the operation of changing the dolly to be carried out more rapidly and shortens the duration of the break in production.
It is further an object of the invention to provide a counter rail to be provided with a dolly, which simplifies the operation of changing the dolly and thus makes it easier to carry out without making mistakes.
It is also an object of the invention to provide a counter rail and a counter rail provided with a dolly respectively, which is easy to manufacture.
According to a preferred embodiment of the invention, it is an object to provide a counter rail provided with a dolly, which eliminates the problem of assembling the counter rail and the dolly in the operation of changing the dolly.
It is a still further object of the invention to provide a cost effective combination module of counter rail and dolly, that functions well both in production and also at maintenance, i.e. in the operation of changing the dolly.
In addition, it is an object of the invention to provide a heat sealing apparatus including the counter rail provided with a dolly according to the invention as well as a packaging machine including such a sealing apparatus.
By manufacturing both the counter rail and the dolly of a plastics material, a less complex construction is achieved at the same time as the two-part module may be integrated to consist of only one single piece. The gains in productivity and cost are considerable, since the sealing apparatus of the invention operates at high speed and every reduction of the time of a production break results in significantly higher efficiency.
The counter rail and the counter rail provided with a dolly respectively, according to the invention is thus suitable for use in a sealing apparatus for transversal heat sealing of a tube of a laminated packaging material filled with a liquid or flowing product, such a sealing apparatus having at least one sealing jaw and at least one counter jaw disposed to face each other and to be movable in advancing and retracting directions for transversally sealing the sealed package, the counter rail being adapted to be included in the heat seal apparatus by being attached to the counter jaw and the dolly being disposed along the counter rail.
Preferred and advantageous embodiments of the counter rail as well as of the module of counter rail and dolly according to the invention have further been given the characterising features as set forth in claims 2-10.
Preferably, from a practical point of view in order not to have to change the counter rail and dolly too often, the plastics should be an engineering plastics having high resistance to chemicals at temperatures ranging from about 10xc2x0 C. up to about 90xc2x0 C., more preferably from about 5xc2x0 C. up to about 100xc2x0 C., most preferably from about 0xc2x0 C. up to about 110xc2x0 C.
Preferably the plastics involved in the counter rail according to the invention, are engineering plastics resistant to alkaline as well as acidic liquids and solutions having a pH ranging from about 2 to about 12, such as for example cleaning agents and sterilising agents normally used for the cleaning of food packaging machines. Advantageously, the plastics employed should also be resistant to hydrolysis when exposed to hot water and aqueous solutions. Furthermore, cleaning agents often contain aliphatic or aromatic solvents, which could be detrimental to some plastics materials. The plastics involved should also preferably be resistant to oil and grease in lubricants, which may be used in the maintenance of the machines. With xe2x80x9cresistantxe2x80x9d is meant that the desired mechanical properties are maintained for a sufficient time when in use.
Among the engineering plastics, polyamides and plastics from the group of high performance plastics (HPP) are particularly preferred. It is well known to the skilled person in the art of plastics that to the group of HPP belongs the polyetherketones, such as polyetherketone (PEK), polyetheretherketone (PEEK), polyaryletherketone (PAEK) and polyetheretherketoneketone (PEEKK), polyphenylenesulphide (PPS), liquid crystal polyesters (LCP), polyimides as well as polysulfones. These polymers generally have some chemical resistance and heat resistance along with good mechanical properties. However, LCP polymers are less preferred since they have limited resistance to hydrolysis. Furthermore, they are less suitable for injection moulding due to their anisotropic properties and morphology. Polysulfones are not preferred either, since they have only a limited resistance to oils and aromatic solvents. Polyimides have limited resistance to alkali while polycarbonates have no resistance to alkali and aromatic solvents, why these polymers also will be less suitable in a counter rail.
The skilled person further knows that to the group of engineering plastics other than the HPP""S, belong, for example, among others, the polyamides, polybutyleneterephtalate (PBT), polyethyleneterephtalate (PET), polycarbonate (PC), polyphenyleneoxide (PPO) and polyoximetylene (POM).
According to one preferred embodiment of the invention, the counter rail is made of a polyamide. Preferably, the polyamide is selected from polyamide-11 (PA-11) or polyamide-12 (PA-12) or a polyamide having similar properties. Generally, the PA-6, PA-66 and PA-46 are less preferred, because they absorb more water and have only limited resistance to acidic liquids and solutions. Polyarylamide (PAA) is not as preferable as PA-11 and PA-12, but still more advantageous than said less preferred polyamides, since they absorb less water.
According to another preferred embodiment, the counter rail is made of a HPP selected from the group consisting of PPS and the polyetherketones (PEK, PEEK, PEEKK, PAEK). The plastics employed in the counter rail according to said preferred embodiments are all resistant to hot water, acidic and alkaline solutions as well as to alcohol, aromatic and aliphatic solvents and oils. Furthermore, they absorb only a low amount of water, generally less than about 1.0%, preferably less than about 0.5%. Moreover, they are suitable and have the right flow properties and mechanical properties for the manufacturing of molded parts such as a counter rail, by means of for example injection molding. It is also important in the choice of plastics for the counter rail, that it has a high degree of dimension stability and that dimensional tolerances may be kept, equal to counter rails made of stainless steel or titanium. The counter rail should preferably have a planarity of less than 0.3 mm, more preferably less than 0.2 mm, and a parallelism of less than 0.1 mm.
According to a most preferred embodiment of the invention, the counter rail is made of reinforced, preferably glass fibre reinforced, PPS. PPS has advantageous properties with regard to chemical resistance, flame resistance, dimensional stability, durability and low water/moisture uptake.
According to a further preferred embodiment, the plastic material in the counter rail may be blended with up to about 50 weight-%, more preferably up to about 40 weight-% of a reinforcement additive, such as for example glass fibres, glass spheres and iron powder, in order to keep the dimensions within the required limits of tolerance. This may be advantageous both from the dimension stability point of view and from the point of view of mechanical properties. However, if the amount of reinforcement additive is too high, the impact strength of the plastic material may be adversely affected.
The dolly employed according to the present invention is made of a thermoplastic elastomer (TPE) having a compressibility of at least about 20% at a Shore A hardness of about 70, as well as high resistance to chemicals and to temperatures of from about 10xc2x0 C. to about 90xc2x0 C., preferably from about 0xc2x0 C. to about 110xc2x0 C.
Preferably, the dolly is made of a thermoplastic elastomer selected from the group consisting of polyurethanes (PUR), polyetherblockamides (block copolymers) (PEBA) and thermoelastic polyolefins (TPE-O). Polyurethanes may be of the polyether-type or of the polyester-type, of which the polyether-type PUR is more preferred. PUR and PEBA generally are more preferred because they are harder and have higher resistance to abrasion, as well as more adequate compressibility for the purpose of a compressible dolly. The TPE polyolefins (TPE-O) have, however, sufficient chemical and water resistance and absorb less than 1.0% water, and are resistant to temperatures of between at least about 10xc2x0 C. and up to about 100xc2x0 C., preferably 110xc2x0 C.
The compressibility of an elastomeric material generally is depending on its hardness, and a PUR thermoplastic elastomeric material generally has a compressibility in the order of about 24% at for example a hardness Shore A of 70, while a PEBA has a compressibility in the order of about 36% at the same hardness. A TPE-O has a compressibility in the order of about 64% at the same hardness.
Most preferably, the counter rail is made of polyamide-11 (PA-11), polyamide-12 (PA-12) or PPS and the dolly of a polyurethane (PUR) of ether-type or of a polyetherblockamide copolymer, because these combinations of plastics, in addition to good mechanical properties and chemical resistance as well as temperature resistance, furthermore result in good bonding and adhesion between the contact surfaces of the plastics at the interface between the counter rail and the dolly.
These specific plastics are preferably used since they allow immediate bonding when consecutively co-injecting the two materials in order to fuse them together. The friction from the high speed of the injected plastics generates heat at the interface between the surfaces of the counter rail and the dolly to be attached to each other, thus resulting in melt-fusion between the surfaces.
Preferably, the counter rail and the dolly are manufactured by means of a co-injection moulding process. By means of so-called co-injection moulding or double injection moulding, the dolly and the counter rail may be manufactured in one operation, the whole piece thus being made of plastics materials.
A further advantage of the counter rail and dolly both being made of plastics materials is that the coefficient of thermal expansion may be matched to be nearly the same, and the difficulties with the combination of metal and plastics materials be avoided. The thermal expansion coefficients of metals and plastics are so different, i.e. ranging from 100 to 200 (10xe2x88x925 mKxe2x88x921) for plastics materials and from 6 to 10 (10xe2x88x925 mKxe2x88x921) for metals. The plastics material is swelling and expanding more than the metal and follows the temperature changes more slowly than the metal. Thus, there must be no surface bonding between a metal counter rail and a plastics dolly. The plastics dolly must be allowed to slide within the groove of the metal counter rail. This, among other factors, makes the shape of the dolly versus the groove so critical. When matching plastics of the same thermal expansion properties for the counter rail and the dolly, these difficulties are reduced or even eliminated and the shape of the dolly and it""s fitting with the counter rail is thus not so critical anymore.
The counter rail and the dolly may be separately injection molded and subsequently attached to each other by means of an adhesive or by means of heat fusion, depending on the combination of plastics material and suitable adhesives available for each plastics material.
Most preferably, though, the counter rail and the dolly are consecutively injection moulded from said plastics materials in a co-injection moulding process and thus attached to each other by melt fusion, which ensures quick, cost-effective and reliable manufacturing of such modules of counter rails provided with dollies in production scale.